Fix various compatibility issues with PHP 8

libs/swiftmailer/preferences.php

@@ -0,0 +1,25 @@
+<?php
+
+/****************************************************************************/
+/*                                                                          */
+/* YOU MAY WISH TO MODIFY OR REMOVE THE FOLLOWING LINES WHICH SET DEFAULTS  */
+/*                                                                          */
+/****************************************************************************/
+
+$preferences = Swift_Preferences::getInstance();
+
+// Sets the default charset so that setCharset() is not needed elsewhere
+$preferences->setCharset('utf-8');
+
+// Without these lines the default caching mechanism is "array" but this uses a lot of memory.
+// If possible, use a disk cache to enable attaching large attachments etc.
+// You can override the default temporary directory by setting the TMPDIR environment variable.
+if (@is_writable($tmpDir = sys_get_temp_dir())) {
+    $preferences->setTempDir($tmpDir)->setCacheType('disk');
+}
+
+// this should only be done when Swiftmailer won't use the native QP content encoder
+// see mime_deps.php
+if (PHP_VERSION_ID < 50407) {
+    $preferences->setQPDotEscape(false);
+}